ABSTRACT: Cataract surgery is the most commonly performed surgery in the United States. Despite this, we know surprisingly little about visual outcomes and rates of complications following contemporary cataract surgery, especially in population subgroups. This lack of knowledge is troubling given that emerging research from Europe suggests that cataract surgery might be ineffective for up to 6% of patients and present significant harms to another 2- 5%. Cystoid macular edema (CME), for example, is a common postoperative complication of cataract surgery. Since the adoption of optical coherence tomography, CME incidence has risen from ~2% to ~40%. However, cataract surgeons lack a clear understanding of what this diagnosis means. To address this issue, we propose a cohort study to generate real-world knowledge about cataract surgery prognosis, including visual outcomes and complication rates; CME diagnostic criteria that correlate with late postoperative vision loss; the prevention of significant CME; and differences in these topics among vulnerable population subgroups. The proposed study will include comprehensive, prospectively recorded data for approximately 186,000 patients and more than 250,000 eyes that received surgery at Kaiser Permanente Northern California from 2007 to 2016. The study will be the largest in the U.S.; will use detailed, comprehensive information that is prospectively recorded into the electronic medical record; and will use modern analytic techniques to ensure valid analyses. The well- characterized, community-based population is diverse, with 29% of patients being non-white and 43% having an ocular comorbidity. Together with the large number of cases, this high level of diversity will enable detailed sensitivity and subgroup analysis. Our results will allow cataract surgeons to individualize care for their patients. The results will also provide desperately needed evidence-based diagnostic criteria for CME. These criteria can be used in research studies, in clinical practice, and to develop practice guidelines. The exceptional volume of cataract surgery justifies research to improve decision-making of this life-changing surgery.